Section 5: Limit of Shunt Indicators

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A form of fixed indicator is usually provided to mark the limit of a signalled shunting movement, where no other suitably located signal exists. This typically applies where a shunting move can be signalled along a unidirectional running line in the opposite direction to normal running moves. Often, an ordinary shunting signal (see Section 3) was provided and fixed permanently in the 'on' position; however, it was the practice of some railway companies to install a distinctive 'limit of shunt' (LOS) indicator for that purpose.

One company that used 'limit of shunt' indicators from an early date was the London Brighton & South Coast Railway. The indicator's appearance was similar to an ordinary working disc signal in the 'on' position (see [3.1]), with the addition of a letter "L" on the red target [5.1].

By 1926, a standard form of 'limit of shunt' indicator had been introduced, bearing the words "limit of shunt" in red on a square white background [5.2]. These indicators were usually ground mounted and were either floodlit or illuminated internally. In some later examples, the background shape was altered to be circular [5.3]. Another variation had the words "limit of shunt" replaced with "shunt limit" [5.4 & 5.5].

There have been rare instances where a signalled move could be made past a 'limit of shunt' indicator. In these circumstances, the LOS (sometimes called a 'secret LOS') must be worked (if mechanical) or extinguished (if illuminated).

A reflectorised design of LOS indicator, with the words "shunt limit" in black [5.6], began to appear in a few places from c.1984.

In 1985, a new standard form of LOS indicator was introduced, which was a derivative of the position light shunting signal. Whereas the ordinary position light shunting signal then in widespread use displayed one red and one white light horizontally as the 'stop' aspect (see [3.83]), the position light type LOS permanently showed two red lights [5.7]. In mechanically signalled areas, a fixed mechanical disc signal (see [3.44]) became the standard form of LOS.

A new design of position light shunting signal introduced in 1996 (see [3.92]) displayed the same 'stop' indication as a modern LOS indicator (two red lights). Consequently, LOS indicators provided in new works are practically indistinguishable from worked shunting signals displaying an 'on' indication.